Experts warn science behind the craze is sketchy – and it can cause harm

In the short term juice diets may lead to headaches, fatigue and dizziness

Long term it can lead to loss of muscle, liver problems and reduced fertility

Whether you are a health aficionado or just keen to get ‘bikini ready’ for summer, you may have already decided to swap solid food for a liquid diet made up of raw fruit and vegetable juice.

If so, you are in good company. Supermodel Kate Moss is known to rely on juicing for last-minute fixes.

In June 2013 she detoxed on nothing but fruit and vegetable juice at a Turkish retreat before doing a Playboy magazine photo shoot.

Spurred by on by promises of ‘miracle results’ including cures for unpleasant conditions like psoriasis and asthma, and of course, fast weight loss, thousands of ordinary men and women are taking up the restrictive juicing diet.

Juicing has become big business. ‘How to’ books outlining juicing diets and regimes are selling in their millions.

Jason Vale, aka The Juice Master, who says he wants to ‘juice the world’, has sold nearly two million copies of his books since he started out on his mission nearly two decades ago.

Joe Cross, another juice crusader and the author of multiple juicing books, starred in his own weight loss documentary, Fat, Sick & Nearly Dead which has been seen by millions around the world.

Both men claim that juicing changed their lives for the better and that everyone can get the benefits of glowing skin, more energy and trimmer waist lines.

In fact, dietitians and food experts are lining up to urge caution about juicing which they say is faddy, ineffective and may even be causing long-term harm.

Migraines have been linked with juicing when whole citrus fruits are often used in the blend.

A 2004 study found when orange juice is squeezed with the rind on, it release synephrine, a vasoconstrictor, meaning it narrows the blood vessels.

There have been links between migraine headaches and synephrine as well as related vasoconstrictors, so it makes sense that this could be a trigger.

Citrus fruits also cause magnesium deficiency in some patients, and magnesium deficiency has been linked to migraine without aura.

Other problems include extreme fatigue, irritability, and constipation.

Those who stick on juicing diets for weeks and even months, not recommended by any of the mainstream diet plans, may be putting themselves at risk of some serious health problems.

‘In the short term, women on these regimes could suffer dizziness, exhaustion and headaches.

‘In the longer term, health consequences could be serious, including problems with fertility, metabolism and even liver damage,’ explained Sioned Quirke, a lead specialist dietitian in obesity and diabetes.

‘Fruit and vegetables contain plenty of essential vitamins and minerals but they are low on important amino acids, fat and protein.

‘The link to sub-fertility and juicing diets is not clear but it is true that women who want to conceive a child need to have optimum health to have peak fertility which you may not have if your on a restrictive diet,’ Ms Quirke said.

Migraine has been linked to low levels of magnesium, which is found in shellfish, beans and pulses but not in great quantities in raw fruit and vegetables.

Ms Quirke added: ‘Other vitamin deficiencies may also trigger headaches. Even temperature changes have been known to cause migraine.

The diet gets results in terms of weight loss but can have unpleasant side effects.

‘Without adequate intake of protein, you can’t maintain muscle mass, so long term juicing can lead to muscle wastage,’ Ms Quirke said, pointing out that every single cell in the body is made up of protein.

Juicing recipes often incorporate algae like chlorella to boost protein levels but these are low compared to other food sources.

Good HDL cholesterol, absent in most juicing regimes, helps to reduce levels of bad LDL cholesterol and ward off heart disease.

The brain is made from long chain fatty acids which are found in oily fish but only occur in avocados in the plant world.

Sue Baic, a dietitan based at Bristol University, rejects the idea that juicing can have a detoxing effect on the body.

‘Detox diets are based on the idea that toxins build up in the body and can be removed by eating, or not eating, certain things.

‘However, there’s no evidence that toxins build up in our bodies. If they did, we would feel very ill.’

Joe Cross, 47, an Australian who now lives in the US, who has also published best selling juicing guides, unsurprisingly also cites his own experience as a good reason for juicing.

Before he decided to ‘face his demons’ he partied hard. The night before his 40th birthday, he downed 10 beers, a bottle of wine, half a bottle of vodka and a packet of cigarettes, or two.

He and got fat until he developed itchy skin condition chronic urticaria all over his body which meant taking powerful steroids to keep it at bay.

‘I was fat, I was sick and I was nearly dead.’ He weighed in at 22 and a half stone at his heaviest.’

But, according to him, thanks to his reboot regime limiting him to juice of fresh fruit and vegetables and a plant-based diet, he regained a ‘perfectly healthy body’, cured his urticaria in the process.

He now weighs 16 and a quarter stone.

Powerful first person testimonies are always convincing and both Joe Cross and Jason Vale are backed by registered medical doctors who are themselves convinced of the benefits.

However, the fact remains that the actual science of juicing is sketchy.

Jason Vales’ juice regimes, which can last five days or seven, are based on his research and experience garnered over more than a decade.

‘I have seen someone at my retreat with Type 1 diabetes reduce their medication by 75 per cent within just the first five days of juicing.’ But there is a distinct lack of hard data published in peer reviewed journals.

‘I don’t really pay too much store by what dietitians say and RDA. In different countries, RDA can vary tremendously and it’s more a matter of opinion than anything else.’

For example, the UK government recommends we all get five portions a day of fruit and veg.

The Japanese RDA (recommended daily allowance) of fruit and veg is 17 different portions.

He doesn’t like to talk about energy intake although typically a day on his 5lbs in 5 days diet will include between 800-1000 calories.

He points out that there are many scientific studies looking at the benefits of certain kinds of juices – for example, according to a study published in the American Heart Association journal, Hypertension, beetroot juice could help to lower blood pressure.

But worryingly, there are no studies looking at the effectiveness of juicing diets and nothing to prove that they cleanse the body.

In particular, there are no contraindications – in other words who shouldn’t take up juicing.

Joe Cross says that although juicing is ‘pretty much for everyone’, there are exceptions. He excludes pregnant women, those undergoing dialysis and chemotherapy as well as those who are underweight or have epilepsy.

He also lists side effects and advises anyone who faints, feels extreme dizziness or low blood pressure to stop the diet and contact a doctor immediately.

It’s this vagueness which can leave him and other juicing gurus open to criticism.

‘It seems to me that there is a lot of spin but not a lot of real facts,’ Ms Baic said.